1. Field of the Invention
The present invention relates to a method for manufacturing chip-like electronic parts and, more particularly, to such a method in which a plating process on external electrodes and various processes required to succeed can be continuously carried out.
2. Description of the Prior Art
FIGS. 5(A) and 5(B) show a monolithic capacitor as an example of a chip-like electronic part 1. The monolithic capacitor has a structure in which external electrodes 4, 4 are provided at both ends of a ceramic device 3 having a plurality of internal electrodes 2 in such a way that the external electrodes 4, 4 conduct with the internal electrodes 2.
The external electrodes 4, 4 each comprise an inside electrode 5 provided by printing or applying a paste such as Ag--Pd, Ag, or Cu to an end of the ceramic device 3 and plating the paste, and a plated layer 6 provided on the surface of the inside electrode with Ni, Sn, solder, or the like for preventing the electrodes from aggression during soldering onto the printed circuit board and for improvement in solderability.
In manufacturing the monolithic capacitor, formation of the inside electrode 5 at the end of the ceramic device 3 is followed by a plating process on the inside electrode 5, a plate drying process, a measurement process for measuring electrical characteristics such as electrostatic capacity and insulation resistance, and a taping process, in this order.
The plating process has conventionally been implemented by using a barrel bath 7, as shown in FIG. 6, into which chip-like monolithic devices and steel balls are accommodated in a certain quantity. The barrel bath 7 is rotated in a plating bath, whereby a plating layer is deposited on the surface of the inside electrode.
The electrical characteristic measuring process has been carried out hitherto in the following manner. A rotary table 8 as shown in FIG. 7(A) is provided with a round hole 9 slightly larger than the diagonal size of the device 3 at regular intervals. The electronic part 1 is inserted into this round hole 9 while it is kept in a fixed position by a bowl-type feeder and a linear feeder. Then the rotary table 8 is rotated, causing a stationary terminal 10 and a movable terminal 11 to move in the direction of arrow a, as shown in FIG. 7(B), so that the external electrodes 4, 4 are brought into contact with the two terminals 10 and 11. In this state, electrostatic capacity, withstand voltage, insulation resistance, and other electrical characteristics are measured.
In this measuring process, the rotary table 8 rotates at high speed, and the productive ability of this measuring apparatus is normally not less than 400 pcs/min. To match the high speed operation, the travel of the movable terminal 11 is approximately 0.5 mm. Therefore, between the electronic part 1 inserted into the rotary table 8 and each of the terminals 10, 11, there is only a clearance as small as approximately 0.1 mm, so that the electronic part 1 rotates in contact with the terminals 10, 11 while the rotary table 8 rotates.
In the above-described conventional plating process, devices 3 would be stirred so as to collide with one another during the rotation of the barrel bath 7. As a result, chips and cracks would occur to the devices 3, and besides the plating layer could not be formed at uniform thickness for the individual accommodated devices, disadvantageously.
Also, since the conventional measuring apparatus requires the electronic part 1 to be fed in a certain position, such a bowl-type parts feeder 12 as shown in FIG. 8 is used. When the parts feeder 12 is used, the same electronic parts move and slide within the bowl many times, causing the external electrodes 4 to be dirtied. These deposits and scratches could cause the measurement of electrostatic capacity to result in false values of capacity. This in turn may adversely affect the measurement of insulation resistance, causing the insulation resistance to lower during the measurement.
Further, in the measuring apparatus, the external electrodes 4 rotate in contact with the terminals 10, 11 while the rotary table 8 rotates. As a result, impulses due to press contact of the terminals 10, 11 may cause scratches to develop to the two external electrodes 4, 4 of the devices 3, or contact with the corners of the terminals 10, 11 may cause chips and cracks to develop to the devices 3.